The present invention relates to pacing and defibrillation medical electrical leads. The present invention also relates to medical electrical leads adapted and configured for implantation within the coronary sinus and coronary veins.
Transvenously inserted leads for implantable cardiac pacemakers have conventionally been positioned within the right atrium or right ventricle of the patient""s heart for pacing or defibrillating the right atrium and/or right ventricle, respectively. While it is relatively safe to insert a pacing or defibrillation lead and its associated electrodes into the right atrium or right ventricle, there is a reluctance to install a similar lead in the left ventricle because of the possibility of clot formation and resulting stroke.
When a lead is implanted within a patient""s circulatory system, there is always the possibility of a thrombus being generated and released. If the lead is positioned in the right atrium or right ventricle, a generated thrombus tends to migrate through the pulmonary artery and is filtered by the patient""s lungs. A thrombus generated in the left atrium or left ventricle, however, would pose a danger to the patient due to the possibility of a resulting ischemic episode.
Thus, in those instances where left heart stimulation is desired, it has been a common practice to use an intercostal approach using a myocardial screw-in, positive-fixation lead. The screw-in lead may, however, be traumatic for the patient. There are additional instances when left ventricular pacing is desired, such as during bi-ventricular pacing. In U.S. Pat. No. 4,928,688, Mower describes an arrangement for achieving bi-ventricular pacing in which electrical stimulating pulses are applied via electrodes disposed on a single pacing lead to both the right and left ventricular chambers so as to obtain a coordinated contraction and pumping action of the heart. The ""688 patent also discloses a split pacing lead having first and second separate electrodes, wherein the first electrode is preferably introduced through the superior vena cava for pacing the right ventricle and the second electrode is introduced through the coronary sinus for pacing the left ventricle. Other electrode leads which are inserted into the coronary sinus have been described. For example, in U.S. Pat. No. 5,014,696 to Mehra and U.S. Pat. No. 4,932,407 to Williams endocardial defibrillation electrode systems are disclosed.
Still other leads and catheters have been proposed, including those described in the patents listed in Table 1 below.
As those skilled in the art will appreciate after having reviewed the specification and drawings hereof, at least some of the devices and methods discussed in the patents of Table 1 may be modified advantageously in accordance with the present invention. All patents listed in Table 1 herein above are hereby incorporated by reference herein, each in its respective entirety.
Prior art coronary vein leads for heart failure applications (i.e., pacing leads) or sudden death applications (i.e., defibrillation leads) generally must be wedged in a coronary vein to obtain a stable mechanical position and to prevent dislodgment. While such an arrangement is generally acceptable for defibrillation leads (which usually must be implanted with the distal tip thereof located near the apex of the heart), such is not the case for heart failure or pacing leads, where more basal stimulation of the heart is generally desired. Basal stimulation of the heart via the coronary vein, however, presents certain difficulties because vein diameters in the basal area of the heart are large and generally do not permit the distal end or tip of a pacing lead to be sufficiently well wedged therein.
Medical electrical leads suitable for implantation within the right atrium and/or right the ventricle are known in the art. Leads having J-shapes imparted to the distal ends thereof are likewise known in the art. Such leads having J-shaped distal ends typically exhibit substantial bending stiffness at the distal thereof, and are most often configured for placement in the right atrium. It is typical that during implantation of such a lead having a J-shaped section at the distal end thereof that, once the lead has been placed within the right atrium, the lead is retracted slightly to impart a positive tip force to the distal end of the lead. Relatively small displacements of the lead in such a manner can result in large variations in the force exerted by the tip of the lead upon the atrial wall. It is therefore not uncommon for the force exerted by the tip to either be excessive or to even become negative, in which event the distal end of the lead is suspended from its own tines or other distally disposed positive fixation device. This, in turn, leads to mechanical instability of the positioning of the distal section of the lead within the right atrium or the right ventricle.
Thus, there exists a need to provide a pacing or defibrillation medical electrical lead which exhibits better mechanical stability following implantation.
The present invention has certain objects. That is, the present invention provides solutions to one or more problems existing in the prior art. For example, various embodiments of the present invention have one or more of the following objects: (a) providing a medical electrical lead suitable for implantation in the right atrium or right ventricle which is not mechanically unstable once implanted therein; (b) providing a medical electrical lead which exhibits enhanced removability following implantation and fibrosis; (c) providing a medical electrical lead suitable for implantation within the right atrium or right ventricle which requires less time and effort to implant; (d) providing a medical electrical lead which exhibits reduced overall stiffness at the distal end thereof; (e) providing a medical electrical lead, the implantation of which exhibits decreased dependency on the longitudinal position of the lead body thereof in the veins leading to the right atrium or right ventricle; (f) a medical electrical lead wherein small dislodgments occurring near the entrance of the lead in the vein near the anchoring sleeve do not lead to electrode tip dislodgment; and (g) a medical electrical lead wherein the width of the J-shape imparted thereto resulting from implantation within the right atrium or right ventricle may vary according to the distance between the electrode position and the location of the superior vena cava.
Various embodiments of the present invention suitable for implantation within the right atrium or right ventricle possess certain advantages, including one or more of the following: (a) exhibiting multiple lead mechanical stability points which exhibit less dependence on positive fixation mechanisms for proper positioning relative to prior art leads; (b) providing a lead whose retention within the right atrium or right ventricle is less dependent upon the particular shape or diameter of such heart chambers and venous anatomy than prior art leads; (c) providing a lead which permits improved pacing electrode positioning within the right atrium or right ventricle; (d) providing a lead which permits lower pacing thresholds and improved sensing of intra-cardiac signals; (e) providing a lead which exhibits improved acute and chronic pacing thresholds and sensing characteristics; (f) providing a lead which has no or reduced positive fixation mechanisms attached thereto; (g) providing a lead which may be implanted with an introducer of reduced size; (h) providing a lead which improves chronic lead removability thereof; (i) providing a straight lead which is easier, more reproducible and less expensive to manufacture; (j) providing a lead which exerts a positive electrode tip pressure or force upon the side wall of the right atrium or right ventricle; (k) providing a lead wherein the tip pressure exerted thereby is less dependent on the specific location of the lead body with respect to the venous anatomy leading into the atrium; (l) providing a lead wherein the depth of the placement of the lead tip into the right atrial appendix may be selectively varied; and (m) providing a medical electrical lead having a stiffness which varies as a function of axial distance adapted for specific placement and stability within veins other than the coronary sinus and great cardiac vein, wherein the lead exhibits appropriate distal curvatures and bending stiffnesses required for implantation within the hepatic vein, spinal column, sub-cutaneously, or in other locations within the human body.
Various embodiments of the present invention exhibit one or more of the following features: (a) a distal section of a pacing or defibrillation lead having variable bending stiffness adapted and configured to create a forward driving force of the lead when the variable bending stiffness portion of the distal end of the lead is subjected to a bending moment resulting in sufficient curvature; (b) a pacing or defibrillation lead having in a distal portion thereof a variable bending stiffness section in which the bending stiffness increases with respect to axial distance; (c) a medical electrical lead which owing to variations in bending stiffness along its axial direction imparts a positive tip force or a forward driving force to the lead, and where bending of the lead may preferentially take place along different pre-determined bending planes (e.g., three dimensional bending along multiple preferred orientations); (d) a pacing or defibrillation lead wherein variations in bending stiffness are rotationally symmetric; (e) a pacing or defibrillation lead wherein bending stiffness is rotationally asymmetric to permit orientation of one or more electrodes, fixation means, or other lead features relative to the bending plane of a bent or curved section; (f) a pacing or defibrillation lead exhibiting variable stiffness over at least distal portions thereof and which is further characterized in having active or passive fixation features, or no such features, being unipolar or multi-polar, being a pacing or sensing lead, being a defibrillation lead, or having a combination of pacing/sensing and defibrillation capabilities; (g) providing a lead capable of implantation within the right atrium or the right ventricle; (h) providing a lead which may be implanted within the right atrium, right ventricle, the coronary sinus, any of the various and/or one or more of the coronary veins; (i) providing a medical electrical lead having enhanced positive tip pressure exerted thereby to promote the transfer of drugs released from the distal tip or a distal portion thereof into the cardiac wall; (j) providing a medical electrical lead having a side arm extending therefrom in a single pass multi-chamber lead, wherein the side arm is employed to pace or defibrillate the right atrium, and wherein the size of the heart within which the lead is implanted assumes less importance is respect of prior art leads because the lead body may assume a greater range of positions within the superior vena cava; (k) in a single pass multi-chamber lead, a medical electrical lead having a side arm extending therefrom for implantation within the right atrium, which side arm may be more easily located along distal portions of the lead body to facilitate orientation and location of the ventricular electrode; and (l) a medical electrical lead employed in conjunction with a pulled wire for imparting curvature to the distal portion thereof to facilitate handling and prevent the electrode from becoming dislodged during the implantation procedure. Methods of making, using, and implanting a lead of the present invention are also contemplated in the present invention.
These and other objects, features and advantages of the present invention will be readily apparent to those skilled in the art from a review of the following detailed description of the preferred embodiment in conjunction with the accompanying drawings in which like numerals in the several views refer to corresponding parts.